I’ll do my best to addres your original questions @Peter_dW
Checkout nextcloudpi.com
No, but there are apps available that offer very basic collaboration from apps.nextcloud.com
Do note that even the Collabora office suite will not be able to support the number of users you describe unless it is run on a more powerful machine. (I find it unacceptably slow on a Pi 4 with SSD disks and one user over 1000mb connection). Checkout this recent podcast where such things are discussed in more detail.
This will work fine once you setup proper SSL to your domain or dynsdns service through NextcloudPi.
NextcloudPi would a prime choice for this.
Fyi, I was able to exceed 1tb of disk space with 2 users in less than 6 months making field recordings as wav and combining with video clips edited in Kdenlive.
The way to prevent this is to set global limits on how much any user can upload, but even then you should expect your disk space will max out in the immediate future between photography and other user data.
In this case your best bet is to use hosted Nextcloud out of a data center. Such solutions will use faster disks on faster networks and allow you to easily scale up as new members onboard.
Unfortunately a Pi 4 will only support around 5 active users. You can try more, but it will not support 30. For that you will need to use a more powerful system.
This will also not be able to accomodate your user base, beyond testing Nextcloud with a few users total.
Do you know how to use SSH and Let’s Encrypt? If you know at least this you’ll have the basics for getting going.
This will require a more powerful system so you can host the High Performance Backend for Talk in Nextcloud, which is the tooling required to support calls of 10+ people. It will not be possible on the Pi 4 with 100mb ethernet.
Pi 4 will work well for this, and you will very quickly outgrow it. Just as easy to use the two month trial on Linode worth $100, which includes data centers in New Zealand and full technical support that is only a phone call away. Set it up with S3 object storage, which you can upgrade at will and also supports one click deployments on Nextcloud. Here is the referral code from a Linux podcast: https://www.linode.com/unplugged
I tried this service and had no trouble signing up or cancelling. You can also call them and ask what plan they recommend for your user base; their support is legit. My experience with them was excellent and it is worlds faster than the Pi or Zimaboard, which you can always use in addition. Good luck! 